Lead frame for semi-conductor device and process of connecting same

ABSTRACT

A lead frame having opposite rows of leads to be connected to the edges of a semi-conductor device and heads on one end of said leads provided with similar angularly related legs between which the edges of the device are received for ultimate soldered connection thereto, the leads and corresponding heads respectively extending from opposite sides of an elongated supporting strip connected at the ends thereof to spaced locations on the lead frame and when the ends of the leads extending from one side of the strip are depressed from the plane of the frame, the ends of the strip where connected to the frame are twisted to extend the headed ends of the leads upwardly and thereby cause the uppermost legs of the heads of opposite rows thereof to be spaced apart a distance greater than the width of the device to be connected thereto while the ends of the rows of lowermost legs of the heads are closer together than the width of the device and receive the same for support thereon prior to the rows of leads being restored to the plane of the frame and thereby cause the opposite rows of uppermost legs to be extended toward each other and overlie the edges of the device and in conjunction with the lowermost legs of the heads secure the device between the legs of the opposite rows of heads.

This application is a continuation-in-part of prior application, Ser.No. 902,798, filed Sept. 2, 1986.

BACKGROUND OF THE INVENTION

This invention relates to a lead frame having rows of leads thereon uponone end of which slit heads are mounted in opposing rows or in a pair oftransversely disposed pairs of rows of heads between which a space isprovided for the reception of a semi-conductor device which comprises asuitable substrate upon which electronic circuits are imprinted eitherupon one or both faces thereof and to which leads are to be connected.When the semi-conductor devices are positioned between the heads on saidrows of leads, soldering of the heads to the ends of the circuits on thesubstrate is effected.

Various problems have been encountered incident to the positioning ofsemi-conductor devices between opposite rows of leads and heads thereonand various attempts to solve said problems comprise the subject matterof the following patents:

U.S. Pat. No. 3,838,984--Crane et al, Oct. 1, 1974

U.S. Pat. No. 4,109,096--Dehaine, Aug. 22, 1978

U.S. Pat. No. 4,196,959--Chesemore et al, Apr. 8, 1980

U.S. Pat. No. 4,234,666--Gursky, Nov., 18, 1980

U.S. Pat. No. 4,323,293--DeRouen et al, Apr. 6, 1982

U.S. Pat. No. 4,496,965--Orcutt et al Jan. 29, 1985

The present invention also is somewhat of a counterpart of applicant'sprior pending application, Ser. No. 648,972, filed Sept. 10, 1984, andoffers certain improvements thereover, without depreciating the subjectmatter of said prior application, as well as over the above-listed priorart, details of which are set forth below:

It is customary in furnishing lead frames to the industry requiring thesame to arrange the same in strip form of indefinite length. The stripsare formed from relatively thin sheet metal, one common form nowemployed being copper of a certain thickness and flexibility. Instamping metal of this type, such as to slit the heads on the end ofleads and bend the legs of the heads apart, for example, to achieve acertain spacing between such legs, it is necessary to bend the legsapart a slightly greater distance than is desired in order that thespringiness of the material will tend to return the legs at leastslightly toward the original position thereof and features of this typehave to be taken into consideration incident to designing finalproducts.

SUMMARY OF THE INVENTION

It is among the principal objects of the present invention to stamp astrip of the type of metal conventionally used, such as certain types ofcopper, to provide a series of lead frame units connected in strip formand each frame unit having rows of leads upon one end of which a head isformed and said rows of leads are provided in spaced oppositerelationship within said frame units of the metal, and in manyinstances, two pairs of opposed rows of said connected leads and headsare provided in the frame, at a right angle to each other, in suchmanner that a substantially square space is formed between the outerends of the heads of all of the rows thereof to receive therebetween asemi-conductor device which ultimately is to be connected to all of therows of heads and subsequently soldered thereto.

Initially, the ends of the legs of the heads which are in opposition toeach other are spaced apart a distance slightly less than the transversedimension of the semi-conductor device to be supported therebetween andthe object of the present invention is to bend the legs of each headinto angular disposition to each other to form substantially a Yconfiguration and parallel rows of the leads and corresponding headswhich are longitudinally arranged therewith are supported by atransverse supporting strip of the same metal which connects the rows ofleads together, preferably intermediately of the ends thereof, and theopposite ends of said strip respectively are connected to certain spacedportions of the lead frame units.

By this arrangement, it has been found that by depressing the outer endsof the rows of leads, which are opposite the headed ends, while the endsof the supporting strip are supported in clamped manner upon a suitabledevice, the opposite ends of said supporting strip are twisted similarlyabout the axis of the strip and all of the leads, in a common plane, aredisposed at a desired angle to the plane of the lead frame. As a resultof such twisting of the ends of the strip to position the leads at saidangle, the heads thereof are elevated sufficiently above the plane ofthe lead frame that the upper legs of each head in opposing rows thereofare spaced apart a distance at least slightly greater than thetransverse dimension of a semi-conductor device to be supported betweensaid heads, while the lower legs of each of the opposed rows of headsare spaced apart a distance less than said transverse dimension of suchdevice, and thus, form a support therefor. Accordingly, when the leadsand heads of opposite rows thereof subsequently are restored to theplane of the lead frame units, the outer ends of the upper legs of theopposite rows of heads are extended toward each other to the initialpositions thereof in which they overlie the edges of the device and thelower legs underlie the device in a manner that they may be connected toterminals of printed circuits upon said device, usually by employingsolder.

Another object of the invention is to bend the legs of the headsangularly away from the plane of the leads to which the heads areconnected, preferably substantially equally in opposite directions so asto subtend an exemplary angle, such as between 30° and 40°, with apreferred optimum angle of 35°, depending upon the thickness of thesemi-conductor devices to be received between the legs of the heads.

Still another object of the invention is to depress the ends of the rowsof leads opposite the headed ends, below the plane of the lead units,and correspondingly raise the headed ends connected thereto at an angleof approximately 40°, for example, to the plane of the lead frame,depending upon the extent of space desired between the ends of the upperlegs of the opposite rows thereof for reception of a semi-conductordevice between the spaced rows of upper legs. The greater the angle ofelevation, the greater will be the space between the ends of the upperlegs of the opposite rows of the heads and the angle between the legs ofthe heads also is a factor controlling the space between the ends of theupper legs of the opposite rows of heads and such angle also must beadequate to accommodate readily the thickness of the semi-conductordevices to be positioned between the opposite rows of such heads but inno circumstances is the space between the ends of the lower legs ofopposite rows less than the transverse dimension of the device to besupported between the rows of heads, regardless of the angle between thelegs or the angle to which the heads are elevated relative to the leadframe units.

One further object of the invention is to firmly clamp portions of thelead frame between opposite clamping members at least in areas adjacentthe opposite ends of the supporting strip and thereby render thetwisting of said ends of said strip more efficient by deflecting membersengaging and depressing below the plane of the lead frame units the endportions of the leads which are opposite the headed ends of the leadsand simultaneously elevate the headed ends of the leads above the planeof the lead frame units.

Still another object of the invention is subsequently to restore therows of leads and heads to the original plane of the frame units, withthe semi-conductor device securely anchored between the opposite rows ofheads, whereby opposite surfaces of said device are availablerespectively to contain separate circuitry connectable selectively tosaid heads and leads of said rows thereof.

Details of the foregoing objects and of the invention are set forth inthe following specification and illustrated in the accompanying drawingscomprising a part thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary frame separated from a strip thereof and showinga pair of opposed rows of leads and heads spaced apart to receive asemi-conductor device therebetween.

FIG. 2 is a fragmentary sectional view taken on the line 2--2 of FIG. 1.

FIG. 3 is a fragmentary section showing a lead frame unit in which twopairs of spaced rows of leads and heads are arranged in 90° relationshipto each other and the ends of said heads are all spaced in such manneras to define the space in which a semiconductor device is to bepositioned and supported.

FIG. 4 is a fragmentary sectional view taken on the line 4--4 of FIG. 3.

FIG. 5 is the first of a series of steps illustrating a method ofmanipulating the lead frame units to effectively and quickly mount thesemi-conductor devices between opposite rows of heads attached to leads,FIG. 5 illustrating the initial position in which a frame unit isclamped between opposed pressing members adjacent opposite ends of thesupporting strips.

FIG. 6 illustrates the next step of the process in which the ends of theleads opposite the headed ends have been depressed by vertically movabledeflecting members to dispose the same at a downwardly and outwardlyextending angle at opposite sides of the frame, thereby spreading theends of the upper legs of the heads a greater distance than initially,while the lower legs are not additionally spaced and are substantiallyadjacent supporting means to receive a semi-conductor device.

FIG. 7 is a view similar to FIG. 6 but in which a semiconductor deviceis shown positioned between an opposite pair of heads and the means bywhich the leads were depressed has been moved to inoperative position.

FIG. 8 illustrates the next step in the method wherein additionalvertically movable presser members are moved upwardly to engage the endsof the leads opposite the headed ends to restore the previouslydepressed leads to the original plane thereof and thereby dispose theupper legs of the heads in overlying position with respect to thesemi-conductor device and cooperate with the lower legs of the heads soas to dispose the heads and device in position for soldering.

FIG. 9 is an enlarged fragmentary detail view showing substantially thepreferred shape of the legs of the heads attached to the sectionallyshown supporting strip, intermediately of the ends of the leads whichhave been foreshortened to accommodate the same to the sheet and inwhich, in full lines, an exemplary position of a fragmentary portion ofa lead frame is shown disposed between the spaced legs of the heads,while in phantom position, the head and lead are shown at an angle tothe original plane thereof and in which the outer end of the upper legof the head has been moved laterally an illustrated distance.

FIG. 10 is a diagrammatic plan view illustrating the relative positionsof clamping members and also deflecting and presser members with respectto each other and the axes of twist of the opposite ends of thesupporting strips for the leads.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION

Referring to FIG. 1, fragmentary lead frame unit 10 is illustrated, itbeing understood that an indeterminate number of such units will beincluded in actual use in a strip thereof. In FIG. 1, only a pair ofopposed rows of heads and leads of a unit are formed to provide a space12 between the rows of heads to accommodate a semi-conductor devicetherein.

Referring to FIG. 3, a lead frame unit 10' is shown as a fragmentarymember of indeterminate length thereof in a strip and in which two pairsof opposed rows of leads and heads are shown to provide a substantiallysquare opening 14 to receive a semiconductor device. In FIG. 1, theleads 16 are shown connected to a supporting strip 18, the opposite ends20 of which are connected to the opposite frame members 22 and 24.Further, it will be seen that the outer ends of the leads 16 arecommonly connected by an elongated member 26.

Referring to FIG. 2, it will be seen that the heads 32, as viewed inFIG. 1, are slit longitudinally to comprise pairs of upper legs 28 andlower legs 30 which, as viewed more specifically in FIG. 9, are shown tobe disposed by an exemplary angle of 35° therebetween, but it is to beunderstood that this preferably is the optimum angle and a range, suchas between 30° and 40°, is operable, depending upon the thickness of thedevices to be engaged thereby.

Referring to FIG. 3, the principal difference over FIG. 1 being that twoopposite pairs of leads and heads are shown respectively at 90° to eachother to form the aforementioned substantially square opening 14 betweenthe outer ends of the rows of heads 32.

Referring to FIG. 4 with respect to FIG. 3, it will be seen that theheads 32 of the upper and lower rows of the heads 32 are spaced apart asare the left and right-hand rows of heads 32. In the initial position ofall of the heads shown in FIGS. 1-4, the ends of the legs of all of therows of heads initially are spaced apart a distance slightly less thanthe transverse dimension of a semi-conductor device to be mountedbetween said rows of heads. A description of the method by which thesemiconductor devices are mounted between said rows of heads isillustrated in FIGS. 5-8, details of which are as follows:

In FIG. 5, it will be understood that while only a single opposed pairof heads is illustrated, they are representative of rows of such heads,as well as the leads 16 to which they are connected. The supportingstrips 18 also comprise pivotal axis 19, see FIG. 10, about which therows of leads 16 are moved by depressing the outer ends of the leads,which are opposite headed ends, to the position shown in FIG. 6 indiagrammatic manner. There is an upper member 34 adapted to facilitatethe placing of a semi-conductor device between opposite rows of heads 32as described hereinafter. Also, fragmentarily illustrated at oppositesides of the member 34 are narrow deflecting members 36 which actuallyengage the ends of the rows of leads 16 opposite the headed ends todeflect the full length of the leads about the axis 19 of the supportingstrip 18, due to only the opposite ends 20 of the supporting strips 18respectively being twisted with respect to the main frame member 10. Ineffect, the portion of the strips 18 to which the leads are connectedmay be said to be rotated about the axis of the strips 18 through alimited predetermined segment of rotation. The narrow deflecting members36 may be moved by any suitable power means in an appropriate cycle withrespect to the lower repositioning members 44.

A lower anvil 38 also is disposed between fixed supporting members 40,the upper ends of which engage and support areas of the lead frameimmediately adjacent the ends 20 of supporting strips 18 and upperclamping members 41 are movable by suitable power means, not shown, toengage upper surface areas of lead frame 10 in vertical alignment withthe areas engaged by lower supporting members 40. Thus, with the leadframe areas immediately adjacent the ends 20 of supporting strip 18firmly clamped, when the aforementioned outer ends of the leads 16 areengaged by the upper deflecting members 36 in descending movement ofpredetermined amount, the ends 20 of strip 18 are simultaneouslysimilarly twisted to dispose the full length of the leads 16 at anexemplary angle to the plane of lead frame 10, as shown in FIG. 6.

In FIG. 6, as a result of the angular disposition of the leads 16,described above, it will be seen that the distance between the ends ofthe upper legs 28 of the heads 32 in opposite rows thereof is greaterthan the transverse dimension of the exemplary semi-conductor device 42,as shown in FIGS. 7-9. Also, as shown particularly in FIG. 7, the outerends of the lower legs of the heads 32 are always spaced apart adistance less than the transverse dimension of the semi-conductor device42, and thus, in addition to the lower anvil 38, comprise a support forthe semi-conductor device 42.

The final step in the operation of the method is illustrated in FIG. 8and in which it will be seen that, while the spaced end portions of thelead frame immediately adjacent the opposite ends 20 of the supportingstrips 18 are firmly clamped between members 40 and 41, when thesemi-conductor device 42 is positioned by suitable operation anvil ofmember 38, the lower legs 30 of the heads 32 and the anvil member 38 aremoved downwardly coincidentally while the repositioning members 44 aremoved upwardly, as shown by the arrows in FIG. 8, and member 34 isdepressed, such upward movement of members 44 restoring the leads 16 andheads 32 to the original position thereof within the plane of the leadframe unit 10, such as shown in FIGS. 5 and 8, with the opposite edgesof the semi-conductor device 42 positioned between the opposite rows ofheads 32 and accurately in position to be soldered to the circuitsdisposed on one or both faces of such device. When this has beencompleted, all of the movable members referred to above are moved to theinitial positions thereof, such as shown in FIGS. 5 and 8 and the stripof lead frame is advanced in the forming device to bring the next leadframe unit thereof into position with the apparatus shown in FIG. 5, andthe above-described method is repeated.

As shown in FIGS. 5-8, supporting strip 18 is indicated between theclamping ends of upper and lower clamping and support members 40 and 41.Actually, the members 40 and 41 engage portions of the lead frame 10which are immediately adjacent the opposite ends 20 of the supportingstrips 18, or possible small portions of said opposite ends, and it isonly the end portions 20 which are twisted to rotate the portions ofstrips 18 to which the leads are connected and thereby dispose the leads16 and heads 32 on one end thereof at the angular positions shown inFIGS. 6 and 7 relative to the plane of the lead frame unit 10.

For purposes of more clearly illustrating and defining to a moredefinite extent than illustrated in FIGS. 5-8, FIG. 9 shows a singleexemplary head 32 with the upper and lower legs 28 and 30 beingillustrated initially, in full lines, within the plane of the main frame10, and when the full length of leads 16 has been transposed from theplane of the lead frame through an angle determined by the thickness ofthe semi-conductor device to be supported between the heads 32, theheads 32 are transposed to the phantom position shown in FIG. 9, whereinit will be seen clearly that there is a marked difference in lateralposition, with respect to the vertical plane of the outer ends of theupper legs 28 of the heads 32, the drawing illustrating solely as anexample for illustration, an exemplary preferred distance of 0.034inches, which when considered in conjunction with the head on anopposite row thereof, not shown, the distance between the upper legs ofthe opposed rows of heads will be increased to the exemplary extent ofapproximately 0.068 inches. This exemplary distance is provided as beingreasonable to accommodate a limited variation in the transversedimensions of semi-conductor devices to be connected to the leadstherefor in accordance with the present invention.

In the designing and constructing of equipment to accommodatesemi-conductor devices of a particular customer, the thickness of thedevices is one important factor, especially in regard to the anglebetween the legs of the heads. Another important factor is thetransverse dimension of the devices to be positioned between the ends ofthe heads of opposite rows thereof, whether a single pair of parallelrows, or two pairs of parallel rows at 90° respectively to each other.Having these critical factors in mind, the angle between the legs of theheads is determined so that the thickness of the devices can readily beaccommodated, and the angle to which the leads are transformed from theplane of the lead frame, by twisting the ends of the supporting strip ofthe leads, is determined to be sure the increased space between theupper legs of opposite rows of the heads is adequate to receive thedevices between the upper legs of said rows of heads while the distancebetween the ends of the lower legs of the heads is not decreased andremains less than the transverse dimension of the devices to besupported by said lower legs of the heads.

Another important feature of the invention is that the terminal portionsof legs 28 and 30 of heads 32 are straight and angularly disposed toeach other at the exemplary angles described above so that there is nofrictional clamping or gripping of the device 42 by the legs 28 and 30,as is clearly shown in FIG. 9, especially in full lines. Therefore, itwill be understood that the illustrative dimensions included above aregiven for a certain specific thickness and transverse dimension of anexemplary device.

After the opposite heads 32 have been moved to the phantom positionshown in FIG. 9, and the semi-conductor device 42 has been mountedbetween opposite rows of said heads, the heads 32 are restored to thefull line position, shown in FIG. 9, by elevating the ends of the leadsopposite the headed ends, and in which restored position the upper legs28 of the heads 32 overlie the edges of the semi-conductor device 42sufficiently to capture the same between opposite pairs of said headsfor subsequent operations, such as connection by solder between theheads and the device supported thereby. The opposite surfaces of saiddevice respectively also are available to support separate circuitryconnectable selectively to said leads.

It will be understood that as the semi-conductor device 42 is positionedupon anvil 38, as shown in FIG. 7 from the phantom position showntherein, and lower repositioning members 44 are elevated, the leads 16will be restored to the plane of lead frame 10 as illustrated in FIG. 8.Also, the lower anvil 38 automatically is coincidentally lowered toprovide adequate support for the device 42 as the heads 32 are loweredto cause the upper legs 28 of the heads 32 to be moved into overlyingposition relative to the edges of the device 42. Upper member 34 alsopreferably engages device 42 from above to insure desired positioning ofit between the opposing heads 32 at opposite edges of the device.

To facilitate understanding of the relative positions of the varioussupport, clamping, deflecting and repositioning members 40, 41, 36 and44, reference is directed to FIG. 10, which is a diagrammatic plan viewshowing in full lines the lower and upper members 40 and 41 which clampthe portions of the lead frame adjacent the ends 20 of supporting strips18, which are shown in phantom dotted lines and longitudinally throughwhich the axes 19 are shown extended to indicate the location of thetwists in the outer end portions 20 of supporting strips 20. Thesuperimposed deflecting and repositioning members 36 and 44 are shown asbeing narrow and of a length corresponding to the transverse extent ofthe rows of leads connected to each supporting member 18.

From the foregoing, it will be seen that the present invention providesadequate apparatus and a substantially fool-proof method of operatingthe same to connect a semi-conductor device between opposite rows ofheads simply by twisting the ends 20 of the longitudinally extendingsupporting strips 18, which connect and support the leads and heads,through an exemplary angle of approximately 40°, the extent of which,however, is controlled by thickness and transverse dimensions ofsemi-conductor devices to be positioned between the opposite rows ofheads, and said angle is operable to space apart the upper legs of theopposite rows of heads a distance adequate to receive between suchspaced upper legs the semi-conductor device 42, within a limited rangeof tolerance of transverse dimensions, and provide ultimate adequatesupport of the semi-conductor device 42 between the opposite pairs ofheads of the rows of leads to be connected to said device in accordancewith the procedures described above and illustrated in the drawings. Theangle between the legs of the heads also is selected to be adequatesuitably to receive the edges of the devices within a limited tolerancevariation.

The foregoing description illustrates preferred embodiments of theinvention. However, concepts employed may, based upon such description,be employed in other embodiments without departing from the scope of theinvention. Accordingly, the following claims are intended to protect theinvention broadly, as well as in the specific forms shown herein.

I claim:
 1. A lead frame for supporting a semi-conductor devicecomprising a metallic planar frame unit having a central opening and atleast a pair of opposite rows of flat leads having heads on one end,each of said heads comprising a pair of similar substantially straightupper and lower terminal leg portions extending from said leads whichleg portions respectively are bent substantially equally in oppositedirections from the plane of said leads in a forked manner, and saidrows of flat leads are connected integrally intermediately of theopposite ends thereof to a flat elongated connecting strip and the endsof all connecting strips surrounding said central opening beingintegrally connected, said connecting strips being parallel to eachother at opposite sides of said central opening and terminal ends of thelegs of the heads in opposite parallel rows thereof are spaced apart adistance less than the transverse dimension of a semi-conductor deviceto be supported by said opposite rows of heads, the opposite ends ofsaid connecting strips are also connected to spaced portions of saidlead frame unit and the intermediate portion of said strips between saidends when rotated about the axis of said strips in one directionsufficiently transpose the plane of the flat leads at an angle to theplane of said frame and thereby elevate the heads of said leads abovethe plane of said frame to space apart the ends of the upper legs ofsaid heads in opposite rows thereof a distance at least slightly greaterthan the transverse dimension of a semi-conductor device to be supportedbetween said opposite rows of heads and the lower legs of said oppositerows of heads extending toward each other a distance no less than whenin the plane of said lead frame, whereby a device is received betweensaid opposite rows of upper legs and is positioned upon said oppositerows of lower legs and said connecting strips and flat leads are thenrotated to restore the same to the plane of said lead frame and saidupper legs of said heads overlie said device and the lower legs of saidheads underlie said device for support and thereby the device is securedbetween the inner ends of the straight terminal leg portions of saidopposite rows of heads for sole independent support thereby.
 2. A planarlead frame unit of flexible metal comprising a substantially flatgeometric pattern of opposed rows of similar flat leads having opencontainment heads respectively on one end of a row of parallel leads ina common plane, portions of the leads of said rows thereof extending inopposite directions from a narrow flat supporting strip connected at theopposite ends thereof to spaced portions of a substantially flat leadframe and the ends of all supporting strips being integrally connected,one end of said leads each having heads comprising a pair of upper andlower legs bent respectively substantially equally in oppositedirections from said common plane to comprise a substantiallyY-configuration with straight angularly related terminal end portions,and the ends of the legs of opposite rows of said heads are spaced aparta distance less than the width of a semi-conductor device which issupported therebetween and the ends of said rows of leads opposite thoseends with the heads thereon when depressed a predetermined distance inone direction from said common plane about the axis of said stripthereby twist the opposite ends of said supporting strip relative tosaid frame and cause rotation of the portion of said strip between theopposite ends thereof and correspondingly elevate said heads of saidleads above the plane of said lead frame and thereby space apartopposite rows of the upper legs of said heads a distance through which asemiconductor device passes and the ends of the lower legs of eachopposite row of heads thereby being closer together than the width ofsaid device and thereby supports said device between said opposite rowsof said heads, and said leads are elevated from a depressed position byreversely rotating said portion of said supporting strip which connectssaid leads, whereby said leads and heads thereon are restored to saidplane of said lead frame and the ends of said upper legs of said headsin said opposite rows are extended toward each other to their originalposition and thereby overlie said device while the lower legs of saidheads underlie said device and secure it between said opposite rows ofheads to comprise the sole support for said devices within said lead. 3.The lead frame according to claim 2 in which said legs of said headscomprise portions of a flat head which is slit longitudinally apredetermined distance inward from the outer end of said head and saidlegs are bent in opposite and substantially equal angles from theinitial plane of said heads and the terminal portions of said legs beingstraight and subtending therebetween an angle of between 30° and 40°. 4.The lead frame according to claim 3 in which the optimum angle betweenthe legs of said heads is substantially 35°.
 5. The lead frame unitaccording to claim 2 further characterized by the heads on opposed rowsof leads being on opposite sides of an opening in said unit and in whichopening said semi-conductor device is disposed when supported betweensaid opposed rows of leads and heads, whereby opposite surfaces of saiddevice are available to contain separate circuitry respectivelyconnectable to the upper and lower legs of said heads on the leads insaid opposed rows thereof.